The present invention relates to a mobile communication transceiver used for a multiple connection access system (to be referred to as an MCA system hereinafter).
In a conventional MCA system employed in Japan, when a non-field condition lasts for more than a predetermined period of time, it is determined that an on-hook condition is satisfied. For this reason, in a mobile radio unit used for the MCA system, a non-field condition is determined by checking whether a given electric field exceeds a certain reference electric field level.
According to another conventional technique, communication is performed by superposing a tone signal on a lower or upper portion of a speech signal band. On a transmitter side, a speech signal is transmitted upon superposion of a tone signal thereon. On the receiver side, the tone signal is detected. If the tone signal is not detected, an on-hook state is determined even if an electric field is present.
According to still another conventional technique, when speech is to be ended, a mobile radio unit transmits an on-hook signal. A radio unit of a callee demodulates and decodes the on-hook signal to determine a speech end.
Of the above-described conventional techniques for determining an on-hook state, in the techniques of determining a non-field condition and superposing a tone signal, since strong waves are present near a repeater station, if a given mobile station approaches the repeater station when a plurality of waves are output from the repeater station, intensity modulation (IM) is performed in the receiver of the mobile station depending on a combination of the plurality of waves. As a result, speech communication cannot be ended by this mobile station due to IM.
In the technique of determining a non-field condition, since an electric field level of the given mobile station at a radio frequency during speech does not become lower than the non-field determination level, the on-hook state cannot be obtained. In the technique of superposing a tone signal, if the same tone signal as that of the given mobile station is superposed on a radio frequency generated by IM during its speech communication, the on-hook state cannot be obtained. However, if the types of tones are increased, errors can be minimized.
In the technique of using an on-hook signal, if the on-hook signal cannot be properly demodulated on the receiver side due to IM, an on-hook state cannot be determined. For example, if an on-hook signal is erroneously converted into different data by signal components due to disturbance from another station, demodulation of an on-hook signal cannot be properly performed.